Rectifier and converter using superconduction



Jan. 19; 1954 A. ERICSSON ET AL 2,666,884

RECTIFIER AND CONVERTER USING SUPERCONDUCTION Original Filed Dec. 2,1948 R1K I R273K 1,0

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RECTIFIER AND CQNVERTER USING SUPERCONDUCTION Original Filed Dec. 2,1948 5 Sheets-Sheet 5 gwue/wboos 333 116 JARVJD ERIC/5503i Patented Jan.19, 1954 UNITED" STATES TENT OFFICE RECTIFIER AND CONVERTER USING U EBCOCTION Eric Arvid' Ericsson, Stockholm, Anders Ossian.

J orgensen,

'rran ber and, Sune Lambert,

Overby, Stockholm, Sweden, assignorsto Tele fonaktiebolaget. L. M.Ericsson, Stockholm, Sweden, a,, Swedish company OriginalapplicationDecember. 2, 1948,. Serial No.

63,052; Dividedvand this application August.

4,1950, SeriaLN IfY'ZJI I bismuth or pure. tungsten can be varied inthe.

relation of 1:100,000 by. means of changes. in a magnetic fieldsurrounding the conductor.

It is also known that the electricalresistance of all conductors at acertain temperature, usual-. ly in the neighborhood of the absolutezero, will decrease to zero (super conductivity). In using a. certainmaterial inthe conductor e. g. columbium-nitride, thiseffect isestablished at a somewhat higher temperature, The. resistance of avso-called super conductor decreases atdecreasing temperature along acurve, the jump curve, which can be situated at different temperaturesin dependence of a surrounding magnetic field.

Theinvention will be described more closely, with reference totheaccompanying drawings, in which:

Fig. 1 shows graphically the relation between the resistance RT 1:. ata. certain absolute temperature and the resistance Rmen. at 273 K. independence of the absolute value. of the field strength H in a magneticfield.

Fig. 2 showsgraphically a juinp. curve that is.

the dependence of the resistance onthe temper-, ature at constantmagnetic field and within a temperature. range where theiconducjtorwissuper. conducting.

Fig. 3 is another jumpcurve showingthede pendence of the resistance onthe magnetic field at constant, low temperaturev Within the. samerange.

Figs. 4, 5 and 6. are sectionalviews of devices for rectifying analternating current.

Fig. 7 shows curves of the dependence of the resistance on the magneticfield (the current) at different absolute temperatures.

Fig. 8 is a sectional view of a device for changing direct current intoalternating current.

Figs. 9 and 10 are views of single phase full wave rectifiers, and

Fig, 11 is a view of a three-phase full wave rectifier.

As already mentioned, the resistanceR of a super. conductor can beinfluenced. as- Well by changing the temperature T as. by changing the.m g cv e d H. as. s shown? 'i ns. of h jumpcurves inliigs. 2.and.3,respectively. It is. thereby of noimportance whether the magnetic 2.field, originatesfrom an outer magnetic field or from the magnetic fieldgenerated by the current in the super conductor. In a; general way, the.change of resistance in.a super conductor is des pendent, on a changeof. the magnetic field and.

the temperature according to the following} ex..- pression:

which showsthe. dependence of the resistance R on: in the first term,changes .of the field strength H at constant temperature, andin thesecond term. changes in the temperature at constant. field; strength H.

In. Fig. 1 the relation between theresistances RT K. and Ra s -K.is.drawn in dependenceon the magnetic fieldJ-I for different absolutetemperaturesTi, T2,. T3, andTi, whereT1 T2 Ts T4 and. the steepness of.the. curveis-greatest at T1 and smallest at T4, thatv is. al a2 a3 a4.It is thus possible to choosea convenient I steepness by choosing asuitabletemperature when. using a super-conductor. as controlling.element.

It appears from. thepreceding, that itis advantageous that the ohmicresistance at the.up per part of, the .jump .curve isas great aspossible, since thereby great. variations. of the. resistance arepossible. as. a 'supenconductor, columbium-nitride, the resistancejof.which atthe upper bend of the jump curve is of, the ohmic; resistance atroom temperature, Whilst the resistance. of pure metal abovethejumpcurve. decreases with the fourth" power of the absolute temperature and.at the. upper bend of. the jump. curve mostly amounts only. to a few,tenths, percent of the resistanceat room temperature. By using not puremetallie super conductors, the useof extreme cooling, for example. by,means. of. cooling with flowing helium, is. avoided. When usingcolumbium nitride, it is suflicienttouse flowing. oxy n as. coolingliquid, which can. be producedmuch cheaper, than. flowing, helium. It.has been proved, that at least partialfsu'per conductivity existsatevenso relatively high temperatures as abovethe boiling point-of liquid air.It is even possible, by..suitable thermic and. chemicaltreat mentof asuper, conductor, to obtain super conduotivity at room temperature.

To .be. suitable for the. purpose. the invention, the-substanceineednotnecessarily besuch, thattheresistanceat the lower part of theusedWorking. curve is=zero. (super-conduction). It is pQSsible muse. cemm'ocm solutions; which.

It. is. therefore advantageous. to use at about -80 have a resistancecharacteristic, which is similar to a normal jump curve, but does not.escend to zero.

Rectifying by means of dry rectifiers is usually obtained by increasingin the blocking direction the normal ohmic resistance which exists inthe flow direction. By using a conductor or semi conductor of abovementioned type as rectifying element, on the contrary, the usual ohmicresistance is arranged to form the blocking direction and means are usedto make the resistance in the flow direction considerably smaller ornear to zero. In such a way it is also possible, having a low resistancein the flow direction, to obtain a practically infinitely greatrectifying relation, if for instance a super-conductor is used asconductor in the flow direction, the specific resist ance of saidconductor being at least the fifteenth power of ten (10 times smallerthan the specific resistance of electrolytic copper.

It is not necessary to obtain complete superconduction in the flowdirection, since a rectifying relation of l 10,000 is sufficient in mostcases. It is therefore possible to use other conductors assuper-conductors, e. g. pure bismuth or pure tungsten, the resistance ofwhich can at low temperatures be changed in the relation 1:100,000 bymeans of changes in the magnetic field.

The two variables T and H in the above equation can be expected tocontrol the resistance, which according to the invention will be usedfor rectifying of an alternating current, and respectively theconversion of a direct current into an alternating current. This isshown in Fig. 2 at constant H and variable T and in Fig. 3 at constant Tand variable H. The embodimerits given below, however, use only one ofthese possibilities, i. e. controlling by variation of the fieldstrength H, since such a controlling seems more advantageous in mostcases, owing to the fact that it can be used up to the highestfrequencies without inertia, whilst thermic controlling is more or lessinert, due, e. g. to heat capacity of the super conductor. Thesediniculties can however be surmounted at lower frequencies.

In Figs. l and 5, two arrangements are shown, in which the resistance iscontrolled directly by means of the current through the super conductor.The temperature of the super conductor is in this case lower than thetemperature at which super-conduction is just obtained Th (1. e. thejump temperature for H=). In the device according to Fig. 4, the superconductor is shaped as a tube 2, the wall-thickness of which is so smallin relation to the diameter of the tube. that it is practically possibleto consider a certain average radius. A field-regulating wire '5 isstretched coaxially in said tube, which wire need not besuper-conducting All of these devices are immersed in a cooling medium 3in a receptacle I with doubie walls, which is provided with a cover 4and a conduit 5 representing the connection with an arrangement forkeeping the temperature and the pressure of the cooling medium in thereceptacle at constant suitable values. Through the field-regulatingwire I a direct current is sent from the terminals 3 having such astrength, Ikr, that the circular magnetic field I-lnof the wire exactlyrestores the ohmic resistance in the tube 2 to normal according to thecurve in Fig. 3. If an alternat ing current is now sent through the tube2 from terminals 5, its magnetic field is superimposed on that of themagnetic field of the wire 1, which,

, 9, as in the design according to 5.

is also circular. If the fields are directed against each other, theresulting field strength decreases, and the resistance more or lessdisappears. This corresponds to the flow direction. When, on the otherhand, the fields cooperate, the ohmic resistance is maintained. Inapparatus for small current strengths, consideration must be taken ofthe earth-magnetic field by introducing screening or compensation. Inorder that the rotary symmetric field be not disturbed, considerationmust further be taken to the lines to the field-regulating wire l, andthese lines be arranged so as not to come too close to the tube. Thescreening may naturally be arranged in a usual manner, but the mosteffective screening is obtained by means of super conductors. Such aconductor is, as known, absolutely diamagnetic and can, when shaped as ascreen, totally bar a magnetic field.

Instead of using a circular magnetic field from a stretched wire I, asis shown in Fig. i, a homogeneous field can also be used. In this case,the super conductor is for instance shaped as a coil At the samestrength of alternating current a stronger magnetic field is obtainedwith this arrangement and it can thus be used for rectifying of feeblealternating currents. A permanent magnet IE3 is used to produce theconstant magnetic field, the working point (Hm) at the upper bend of thejump curve therefore being set by means of the temperature. If anelectromagnet is used, the working point can be set as well by thermicas by magnetic means, which can be an advantage in such a device forrectifying with amplitude limitation, as is described below. The arrangement of the receptacle and cooling medium in Fig. 5 are the same as havebeen described in connection with Fig. 4..

Instead of establishing the rectifying effect exclusively by means ofthe magnetic field generated by the super conductor itself, an auxiliarycoil can be used according to the design shown in. Fig. 6, where theouter devices for producing a suitable temperature are the same as inFigs. 4 and 5. The super conductor, shaped as a coil II, is bifilarlywound to prevent the generation of a magnetic field, and its resistanceis thus not influenced by current flowing through it. A direct currenthaving such a magnitude, that a suitable working point Hm is produced,is fed by means of a coil I2, wound coaxially to the coil H round thereceptacle I. A further coil I3 is applied coaxially to the other twocoils. A source of A. C. potential is connected to said last coil. Themagnetic field of the last coil is positively or negatively superimposedover the direct current field from the coil i2, whereby the resistancein the super conductor, which forms the coil 5 I, varies between zeroand ohmic resistance. If the currents through the coils i! and it havethe same frequency, a rectifying of the current through coil 5 l is thusobtained. If the currents have the same frequency but the current incoil I3 has another curve shape than the current in coil H, thecurve-shape of the rectified current is changed through coil H.

The device shown in Fig. 6 can be used to transform direct current intoalternating current. The direct current, which is to be transformed,flows through coil H. An alternating current having the desiredfrequency is sent through coil [3, which current furthermore has acurrent intensity which, at the given numbfil' of turns in coil 13,generates a field, which accuses;

makes the coil H alternatively supemconduct ing and normalconducting.The arrangements according to Figs. 4- and can also aftersuitablechanges be used-to transform direct current-into alternatingcurrent asissuggestedin the connection according to Fig. 8, which showsamodi fication'of the device according to Fig. 5; The latter design hasbeen completed-'withtwocoils l2=- and I3 on the magnetlil'; which coilscorrespond to-the coils i2 and t3 in'-the---device=ac-- cording to Fig.6. Thedirect current generated by a source it oi directourrent'istransformed into alternating current and can betaken outover atransformer atthe terminals *8.

Rectifying by means of superconduction ac-* cording to the inventioncanbe 'combined with amplitude limitation. A-s-is' illustrated in Fig.'7,

the jump curves for positively ornegatively-di rected" currents Iforcorresponding tempera tures T1, T2. relation to the line 1:6;

value, which increaseswith decreasing tempera- .l

ture towards'a limit value. By regulating the number of ampere-turns inthe coil II of Fig. 6 and the temperature, it" ispossible to produce anamplitude limitation, which can be regulated.

The device according to the invention can" also be built as a two-phase.rectifier in bridge: connection. A design of such a connection is shownin Fig. 9. Devices for cooling oithesuper conductors are not shown intheschematicdrawing. They are supposed to be: made in a waywhichisillustrated in principle in Figs. 4", 5, 6' and 8. The principle ofrectifying for each rectifying member is the. same as has been describedin connection with Fig. l. Thebridge comprises four rectifying members,out of which two and two are directed in the same direction. In theshown device, they are united so that only two super conducting. tubes253; 21 with middle-point tappingare .used; Such a tube with itsfield-regulating wire. 251' acts in the shown arrangementastworectifiers connected in series and can be used as such an aggregatealso in other connections and relations.

The ends. of the tubes 2e, 2.! are inter-connected and form a pair ofterminals 22, from which. the rectified current can be taken out. Thealternating current is. fed at themiddle pointsof thesuper conductingtubes 28, 2 from a source of alternating current connectedto a pair ofterminals: In order tolprevent said current from deforming the circularfield around the tubes 2%, 24 from the coaxial field-regulating wires26, 2'? (corresponding to i in Fig. 4), the;

connection to the tubes 29; 21 from the pair of terminals 25 is obtainedby means of. large. con.- centric cylinders 23, 2 3" placed round saidtubes and connected to the tubes 2d, 2! by means of flanges 29, 3%,respectively. Since the connections thus become rotary symmetricalrelative to the wire 2% and 2?, they cannot disturb the circular fieldof said wires. The wires 23, 21 are connected in parallel and connectedwith a pair of terminals 28 to which a source of direct current (notshown) is connected. The desired working point Hkr (Figs. 5 and '7) canbe oba. s; 0;, lie symmetrically irr- If," forinstance, the workingpoint Hinatthe upper'bend of the jump If the amplitudes" are 6 tained.by. adjusting the intensity of the current from said'source:

In Fig. 10; anotherdesignof-a rectifying bridge according tothe-invention is shown. All the rectifying; members (the tubes 20; 2'!in' Fig. 9) are in'thissembodimentaunited and. bent to a superconductingtube-ring 30 with a. field-regulating' wire 31 applied coaxially in thetube, thereby. forminga continuous ring. Two diametrically opposedpoints oat-11c: wire; 3! are connected. to:. a. pair. of terminals, 23,. representing a scurce'of" direct: current'which; can; be regulated.The aiternatingacurrent, which has to be rectified, is fedpatzzthe-pairof terminals 25,.

which are connectedito'. two points jlying opposite each other on thetube-ring-3O, and which are outoi phase relatively tothe connections-tothefield'regulating.wire iii; From. the ring 30- close to said wireconnections the rectified alternating currentlisitaken out Home pair ofterminals 22.

Each one: of'the partsof the tube lyingbetween the connectionpoints'acts as a rectifying member. If thesouroe-of' direct current isconnected to the terminals 23'with a polarity. shown on the drawing, allthe members (as. is illus-. trated with dotted symbols. 32.) have their.flow direction upwards, since flow. is obtained in. members, where thefieldirom the currents from the terminals 25 and 28- counteract eachother; The blocking is obtained when said currents cooperate. Theconnections to the tube is are made as rings round the tube. To preventthe circular field from-the-wire 3'! from being dis-- i tu'rbedbythe:connections to said: wire and to thetube, measuresanalogous to: thoseinFig. 9 can be taken.

In Fig. 11, athree-phase full-wave rectifier is connected to aA-connected secondary winding 3 in a transformer. Thedevicecomprisesthree full-wave rectifiers, each of' which consists of twomembers connected inseries, which. both have-flow direction-to-the leftat the mentioned polarity of the source oi controlling current at thepair of terminals 23. terminals are as iii-Fig. lO-connected to theparallel connected field-regulating wires 3-1; 38 and 39, respectively,in theconduc-tingtubes 34, 36'. The threephase winding 33 carrying thecurrent to be rectifled, is connected withone phase to the middle ofeach' tube. The-direct current is taken from the end-points ofthetubesin parallel and conducted to a pair of terminals 22 In the devicesaccording to Figs. 10 and 11, the superconducting; tubes are supposed tobe immersed in a medium keeping the temperature at a" suitable constantvalue to. produce the desiredsuper conducting properties.

For-theabovedescribed rectifying purpose thefollowing conductors aresuitable: (a) super conductors, which are not chemical elements, (27)semi-conductors, (c) non-stoichiometric connections, and (d) metallicsolutions, in which the super properties appear at temperatures, whichare not too low, and their resistances at the upper bend" of thejumpcurve is a rather great part of the resistance at room temperature.

This application is a division of our copending application Serial No.63,052, filed December 2, 1948.

We claim:

1. Apparatus for rectifying alternating current comprising incombination, a conductor, means to maintain the temperature thereof at alevel substantially that at which superconduction is obtained, means tosurround said conductor with a constant magnetic field having anintensity such as to substantially restore the ohmic resistance of theconductor to normal, means to surround said conductor with a magneticfield having a variable component and means to pass the alternatingcurrent to be rectified through the said conductor, said variablecomponent being in synchronism with said alternating current.

2. Apparatus for rectifying alternating current comprising incombination, a conductor for the said alternating current and in whichit is rectified, apparatus for changing the resistance of the conductorin synchronism with said current and at least in the ratio of 1:10,000,said apparatus including means to reduce the temperature of theconductor, means to surround the conductor with a magnetic field, saidlast means being regulated to cooperate to bring the conductor to acondition where a small change therein produces a resistance change ofthe stated ratio and an instrumentality to effect such small change inthe condition by adjusting said last means in synchronism with. thealternating current in said conductor.

3. A rectifier including in combination, a concluctor in whichalternating current flows and is rectified, means to reduce thetemperature of the conductor to a point within a range where theresistance changes in a ratio of at least 1:10,000, means to surroundthe conductor with a biasing magnetic field and said conductor beingsurrounded with a reversing magnetic field which alternately augmentsand opposes the first field in synchronism with the said alternatingcurrent.

4. The rectifier as defined in claim 3 in which the reversing magneticfield is produced by the current in the conductor itself.

5. The rectifier as defined in claim 3 in which said conductor comprisesa tube traversed from end to end by the said alternating current toprovide the reversing magnetic field and a wire carrying direct currentpassing coaxially through said tube to provide the biasing magneticfield.

6. The rectifier as defined in claim 3 in which said conductor formed asa wound coil to provide the reversing magnetic field by the alternatingcurrent which fiows in it.

'7. The rectifier as defined in claim 6 in which the constant magneticfield is formed by a permanent magnet.

8. The rectifier as defined in claim 3 in which the conductor is formedas a bifilar winding, a coaxial winding energized by direct currentforms the biasing magnetic field and a coaxial winding energized byalternating current of the same frequency as that in the conductor formsthe reversing magnetic field.

9. The rectifier as defined in claim 8 in which the wave-forms of thealternating currents in the conductor and last mentioned windings aredifferent.

10. The rectifier as defined in claim 3 for full Wave rectification inwhich the conductor comprises a number of tubes, means connecting themid points of said tubes to the alternating cur rent source forrectification and for producing the reversing field, and meansconnecting corresponding ends of tubes each to one side of a directcurrent output.

11. The rectifier as defined in claim 3 for full wave rectification inwhich the conductor comprises a number of tubes, means connecting themid points of said tubes to the alternating current source forrectification and for producing the reversing field, means connectingcorresponding ends of said tubes each to one side of a direct currentoutput, and conductors coaxially arranged in said tubes and energized bydirect current to provide the biasing field.

12. The rectifier as defined in claim 3 in which the conductor is formedas a toroidal tube, a direct current energized conductor within saidtube, alternating current input terminals at 180 spacing on said tubeand direct current output terminals spaced at mid points between thefirst terminals.

13. Apparatus for rectifying alternating current comprising a conductor,means to pass alternating current to be rectified into said conductor,means to maintain the temperature of the conductor within apredetermined range, means to surround the conductor with a steadymagnetic field in a predetermined intensity range, said range beingselected whereby a small change Within either will cause a resistancevariation within the conductor of the order of at least 1:10.000, andmeans acting in unison with the pulsations of said alternating currentto alternately oppose and augment said magnetic field to effect saidchange.

14. Apparatus for converting direct current comprising a conductorconnected to a source of direct current, means to maintain thetemperature of the conductor within a predetermined range, means tosurround the conductor with a steady magnetic field in a predeterminedintensity range, said ranges being selected whereby a small changewithin either will cause a resist ance variation within the conductor ofthe order of at least 110,000, and means to alternately oppose andaugment said magnetic field at the frequency of the desired alternatingcurrent.

ERIC ARVID ERICSSON. ANDERS OSSIAN J ORGEN SEN. SUNE LAMBERT OVERBY.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,579,448 Smith Aug. '7, 1923 1,765,607 Ohl June 2%, 19301,810,539 Sockoloff June 15, 1931 OTHER REFERENCES Communications fromthe Physical Laboratory of the University of Deiden, by H. K. Onnes, No.139(f), pages -71, 1914; esp. page 67.

Bureau of standards Bulletin, vol. 14, pages 301-306, by F. B. Silsbee,1918; esp. page 302.

